Protease or Clostridium butyricum addition to a low-protein diet improves broiler growth performance

Low-protein (LP) feeds are used in the poultry industry to combat the increasing consumption of protein resources and reduce environmental pollution caused by excessive nitrogen excretion. Dietary supplementation of protease or Clostridium butyricum increases the growth performance of broilers; however, it is unclear whether they counteract the negative effects of LP diets. The effects of protease and C. butyricum on growth performance, intestinal morphology, anti-oxidant capacity, anti-inflammatory response, and microbial community of broilers have not been studied extensively. Here, 450 healthy 1-day-old Cobb500 broilers were allocated to five groups, according to different diets: basal diet (Control); LP diet (LP; 2% less crude protein than the control); LP diet + 200 g/t HuPro protease (LPH); LP diet + 1.0 × 10⁹ CFU/t C. butyricum (LPC); and basal diet + 200 g/t oxytetracycline (Antibiotic). Supplementing both C. butyricum and protease improved the growth performance of broilers. The supplementation of HuPro protease under low-protein conditions could achieve a breeding effect similar to that of the positive control (Antibiotic). Supplementing C. butyricum could maintain intestinal barrier function, alleviate the inflammatory response, and increase ileal and cecal short-chain fatty acid concentrations. Both C. butyricum and protease altered the bacterial diversity in the cecum, increased Bacteroidetes abundance, and resulted in higher abundance of Rikenellaceae RC9 gut spp. and lower abundance of Alistipes spp. in broilers. This study demonstrates the positive effects of proteases and C. butyricum on broilers and serves as a reference for the selection of appropriate supplementation for broilers in the poultry industry. KEY POINTS: • Low-protein diet had a negative effect on growth performance of broilers. • Protease significantly reduced feed conversion rate. • Clostridium butyricum had positive effects on broilers.